Previously, there is known an electric motor that drives a drive subject installed at a lower side of a vehicle. For example, in a case of an electric motor disclosed in JP3716127B2, an antilock brake apparatus is a drive subject of the electric motor. This electric motor is installed at the lower side of the vehicle, so that a seal member, which is shaped into a ring form and is made of rubber, is installed between a case of the electric motor, which is shaped into a tubular form having a bottom, and a housing of the antilock brake apparatus, to limit intrusion of water into an inside of the case of the electric motor. A frame, which closes an opposite side of the case that is opposite from the bottom of the case, is placed in the inside of the case, and there is no seal member between the case and the frame. In the electric motor of JP3716127B2, the number of seal member(s) and the number of sealing location(s) are reduced in the above described manner.
In the electric motor of JP3716127B2, the case is formed through a press work of a deep drawing quality cold rolled steel plate (e.g., SPCE) into the tubular form having the bottom. Furthermore, since the frame is configured to be fitted to the case, it is assumed that the frame is made of iron. In contrast, the housing of the antilock brake apparatus is made of metal and is formed as a solid block body, so that it is assumed that the housing of the antilock brake apparatus is an aluminum die-cast product.
In the electric motor of JP3716127B2, since a wall thickness of the case is small, it is difficult to form a seal groove, which receives a seal member, at the case. Thus, a selection of an installation subject may possibly be narrowly limited.
Furthermore, in the case where the seal member is compressed with the case having the small wall thickness like in the case of the electric motor of JP3716127B2, there is a possibility of that the case is deformed by a reaction force of the seal member. Therefore, there is a possibility of that the sealing performance is deteriorated at a circumferential location(s) of the case. Furthermore, when the case is formed by the press work, a degree of flatness of a seal surface of the case is relatively low. Therefore, it may be difficult to increase the sealing performance of the seal member.
Furthermore, in the electric motor of JP3716127B2, since the case is made of the steel plate, it is required to apply a surface treatment for limiting generation of rust at an outer wall of the case.